The primary purpose of the proposed research is to extend our understanding of perceptual development, both normal and abnormal. A series of experiments is proposed to examine age-related and experience-induced changes in auditory perception. The pervasiveness of normal developmental trends involving increasing perceptual specificity both within and between perceptual dimensions, will be documented with both pure-tone and species-specific stimuli. The specific effects of normal experience as well as the conditions necessary and sufficient for normal development will be deduced from deprivation studies. The contributions of peripheral and central nervous system changes to these effects will be determined by physiological studies. The research strategy will be to thoroughly examined ontogenic and experientially mediated changes in one organism (the avian hatchling), in one sensory system (audition) and principally along one physical dimension (frequency). The primary dependent measure will be suppression of vocalizations following changes in acoustic stimulation. The amount of that suppression will be used as a measure of the degree to which the animals distinguish changes in auditory information. Previous research has shown that this response changes with age and experience as predicted by current theories of perceptual development: differential suppression is elicited by progressively smaller changes in frequency over the first few days of life; and deprivation of normal acoustic experience disrupt this development.